Lubricating oils form interfacial films between moving metallic parts. These oils typically contain one or more of the following additives: boundary additives, corrosion inhibitors, anti-oxidants, dispersants, anti-wear additives, and extreme-pressure (“EP”) additives. Boundary, antiwear, and extreme-pressure additives are typically grouped as performance additives while the others as functional additives. This invention pertains to the synthesis and use of nitrated extreme-pressure additives.
Among the performance additives, the primary function of a boundary additive is to reduce friction generated by metal-to-metal rubbing. These additives can be fatty oils, fatty esters, soaps consisting of oxygen-containing functional groups and long-chained hydrocarbons. They are only effective up to temperatures of approximately 150° C. and are therefore effective and useful only for light-duty operations involving soft metals such as copper or aluminum, or light-duty applications involving cast-iron or steel.
For a medium-duty or moderate loads processing steel, low levels of sulfurized additives and/or anti-wear additives such as ZDDP (zinc dithiophosphates), or phosphate esters and phosphites are typically employed. These phosphorous-based compounds are effective up to around 300° C. but lose their effectiveness at higher temperatures.
For heavy-duty applications involving hardened steel, particularly at higher speed and loadings, the extreme-pressure additives such as sulfurized and chlorinated additives have traditionally been employed. These species react with metal surfaces at much higher temperatures ranging from 350° C. for chlorinated additives and from 500° C. for sulfurized additives. Through chemi-adsorption with the metal, these additives form a sacrificial coating to prevent not only wearing, but also welding or adhesion between two dissimilar metal surfaces, such as a die and a work piece.
Presently, commercial extreme-pressure additives contain one or more sulfur, chlorine, or phosphorus-containing compounds. Sulfur-containing additives are sulfurized fat or fatty esters or synthetic polysulfides; chlorine-containing additives are chlorinated paraffins, olefins, or chlorinated fatty compounds; while phosphorus-containing additives consist of phosphate esters and phosphites. Each of the above-mentioned commercial extreme-pressure additives has its own set of limitations.
Sulfurized additives are effective for working with steel parts but not those involving stainless steel or special alloys such as titanium, chromium, or nickel-based, especially those in the most severe working environments. Phosphate esters or phosphites are excellent anti-wear or load-carrying additives but only in light-duty applications. For most cases, they are not effective extreme-pressure additives and definitely unsuitable for applications involving stainless steel. One of the reasons is that these phosphorus and sulfur-containing additives are not very reactive to hardened steel or low-iron metallic composites such as stainless or special alloys mentioned above. Chlorinated compounds, on the other hand, are very effective in wide range of metal processing applications involving both steel, stainless steel, and special alloys. The rule of thumb in the industry is that chlorinated additives are required for working with these exotic alloys of low or no iron content. However, recent environmental concern regarding the disposal of chlorinated compounds has prompted the lubricant industry to search for alternatives to replace the chlorinated additive workhorse.
This invention describes a novel class of extreme-pressure additives, labeled generically as “nitrated” or nitro compounds. The nitro compounds cited in this invention can be made by using 70% nitric acid or nitrogen dioxide gas to nitrate many classes of compounds, such as: (1) fatty acids with unsaturation; (2) fatty oils which contain unsaturation sites on their hydrocarbon chains such as vegetable oils, tall oil and animal fats; (3) esters (synthetic or natural) derived from the reaction of alcohols with fatty acids, such as triglycerides; (4) C2-C28 simple terminal or internal olefins, more preferably C8-C18 olefins; (5) C2-C20 polyolefins or C4-C20 polydiolefins, more preferably C2-C6 polyolefins containing terminal or internal unsaturation, preferably polyisobutylene (hereinafter “PIB”); (6) C8-C20 copolymers derived from polyolefins and vinyl aromatics e.g., poly(styrene butadiene); and (7) C4-C30 alkylated phenols, e.g., nonyl phenol and wherein the alkyl group is a straight or branched chain.
At least one novel feature of this additive is that it contains nitro-compounds instead of conventional elements such as sulfur, chlorine, or phosphorus, and has demonstrated its effectiveness as an extreme-pressure additive capable of replacing (either completely or at least partially) both sulfurized chlorinated, and phosphated additives for both steel and stainless steel applications, for aluminum applications, as well as for processing metallic alloys which are currently considered as most challenging such as titanium, nickel, and chromium-based metals or alloys.
U.S. Pat. No. 4,076,738 describes how to make polyisobutylene carboxylic acid by reacting ozonized polyisobutylene with nitric acid for use in the area of fuel and gasoline additives.
U.S. Pat. No. 4,347,148 describes a process of preparing nitro-phenols by reacting polyisobutylene-substituted phenols with nitric acid in presence of sulfuric acid or a Lewis acid. The nitro-phenols were indicated to be useful as fuel dispersants in combustion engines.
U.S. Pat. No. 4,410,746 describes a process preparing nitro-olefins comprising reacting a nitro diol with an aldehyde acceptor in the presence of a catalyst. Such nitro-olefins can be used as solvents or pesticides.
U.S. Pat. No. 5,103,061 describes a nitration process of polyisobutylene (“PIB”) using nitrogen oxides gas and subsequent derivatives to generate fuel additives.
U.S. Pat. No. 5,454,842 describes an esterification process of fatty alcohols derived from the reduction of tall oil fatty acid and vegetable oils with nitric acid. The obtained product is a nitrate and the end use is cetane improver for diesel fuel.
U.S. Pat. No. 6,069,281 describes the nitration process of polybutenes or polyisobutylene with nitrogen oxides and further processing with hydrogenation to produce polyamine derivatives for fuel additives.
U.S. Pat. No. 6,362,381 B1 describes the nitration of aromatic hydrocarbons with oxides of nitrogen, an oxygen-containing gas and an oxidic catalyst. The described end use is in the area of fuel additives.
U.S. Pat. No. 6,888,030 B2 describes a process of producing polyamines by hydrogenation of nitrated polyisobutylenes in the presence of a branched alcohol, using 70% nitric acid. The end use for the invented product is fuel additives.
Unites States Patent No. 2001/0037598A1 describes a process of nitration to produce nitrated methyl esters derived from vegetable oils. The final product is a nitrated compound and not a nitro compound as illustrated in the current invention. Additionally, the published application teaches an end use for the nitrated methyl esters as cetane improvers for diesel fuel.
This invention describes a novel class of oil-based as well as water-dispersible extreme-pressure additives, labeled generically as “nitrated” compounds. In one embodiment, these additives can be used synergistically with at least one non-chlorine containing additive. At least one novel feature of the nitrated additive is that it contains no or reduced amounts of conventional elements such as sulfur, chlorine, or phosphorus, and has demonstrated its effectiveness as an extreme-pressure additive capable of replacing or partially replacing sulfurized, phosphated, and primarily chlorinated EP additives for both steel and stainless steel, as well as the above-mentioned non-ferrous applications.